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Solvent effects were investigated for selective hydrogenation of acetophenone (AP) with commercial 5% Pd/Al2O3 and 5% Pd/C catalysts using polar and nonpolar solvents. The rate of AP hydrogenation varied with the solvents used in different ways depending on the catalysts used. The highest AP conversion was achieved with water for the two catalysts and the AP conversion was correlated with hydrogen-bond-acceptance (HBA) capability (β) for Pd/Al2O3 and hydrogen-bond-donation (HBD) capability (α) for Pd/C. These trends were the same as the corresponding solvent effects obtained previously with Rh/Al2O3 and Rh/C catalysts, respectively (Green Chem., 2015, 17, 1877–1883). The influence of solvents on the rate of AP hydrogenation depends on the support materials and not on the metal species. Furthermore, AP hydrogenation was conducted with the four supported noble metal catalysts in different solvents pressurized by CO2 (CO2-dissolved expanded solvents). The influence of CO2 pressurization on the rate of reaction, the product selectivity, and the catalyst life was investigated to know whether or not CO2 molecules could function as a reaction promoter in heterogeneous AP hydrogenation reactions with supported Pd and Rh catalysts in different solvents. [ABSTRACT FROM AUTHOR]

The selective hydrogenation of benzyl cyanide (BC) to the primary amine of 2-phenylethylamine (PEA) was investigated with a Pd/Al2O3 catalyst in different multiphase reaction media including n-hexane, water, and/or CO2. In neat n-hexane, the hydrogenation of BC occurs at a large rate but no PEA was formed and the secondary amine of N,N-bis(2-phenylethyl)amine (BPEA) was produced as the main product. The pressurization of n-hexane with CO2 decreased the rate of hydrogenation and the main product was BPEA. In this n-hexane–CO2 medium, the catalyst lost its activity during the reaction. When a similar volume of water was added to n-hexane, the rate of hydrogenation did not change so much but a small amount of the primary amine was detected to form in addition to the main product of BPEA. In contrast to these reaction media, a high PEA selectivity of ＞90% was obtained and no catalyst deactivation occurred in an n-hexane–water–CO2 medium. The rate of hydrogenation was smaller than that in neat n-hexane but comparable to those in n-hexane–water and n-hexane–CO2 media. Those results show that synergistic effects appear on the selective hydrogenation of BC to PEA when both water and CO2 are included in the reaction medium. Possible roles and actions of water and CO2 have been discussed on the basis of the results of hydrogenation runs under different conditions and in situ ambient and high pressure Fourier transform infrared spectroscopy measurements that give insights into molecular interactions of CO2 with reacting species. [ABSTRACT FROM AUTHOR]

Highlights: [•] Au–Pd/TiO2 were synthesized by the single step flame spray pyrolysis. [•] FSP resulted in more uniform and smaller Au–Pd particles compared to IMP and DP. [•] Rate of 1-heptyne hydrogenation depended on Pd dispersion and location. [•] Selectivity to 1-heptene was greatly modified by the presence of Au–Pd alloy. [ABSTRACT FROM AUTHOR]

Highlights: [•] CO formed on Pd surface retards the adsorption of phenol. [•] Cyclohexanone is preferentially adsorbed on Pd than CO and water. [•] The leaching of Pd occurs and the potential of Pd surface gradually changes in hot water. [•] The catalyst deactivation occurs rapidly in the presence of both dense phase CO2 and water. [ABSTRACT FROM AUTHOR]

Highlights: [•] Calcination of sol–gel TiO2 under H2 created more surface Ti3+ than in air. [•] Catalyst performance in selective acetylene hydrogenation improved using TiO2-H2. [•] Higher Pd dispersion and more isolated adsorption sites were obtained on TiO2-H2. [•] The catalysts were prepared by impregnation and electroless deposition techniques. [•] The effectiveness of TiO2-H2 was confirmed for both methods and Pd 0.5–1wt.%. [Copyright &y& Elsevier]

Abstract: TiO2-supported Pd–Au catalysts were prepared with Pd (0.5 wt%) by impregnation and then Au (1.0 wt%) by deposition–precipitation (Au/Pd/TiO2) and vice versa (Pd/Au/TiO2). For the former sample, the state of dispersion of Pd on TiO2 changed during the loading of Au, resulting in the formation of small Au–Pd alloy particles and thus changing the electronic properties of Pd species. The alloy formation was not clearly detected on the Pd/Au/TiO2, and the electronic properties of Pd were not so different from those of monometallic Pd/TiO2. All the catalysts were selective to 1-heptene (>95%) until close to the complete conversion of 1-heptyne. However, the selectivity of 1-heptene drastically decreased to 0% (which was further hydrogenated to heptane) in 120min for the Au/Pd/TiO2 while it still remained >60% for the Pd/Au/TiO2 similar to the monometallic Pd/TiO2 catalyst. The rate of 1-heptene hydrogenation (in the second step) did not depend on the Pd dispersion but was found to be greatly enhanced as the Pd species became electron-rich in the Au–Pd alloy particles. The modification of Pd species by Au was less significant for the first step of hydrogenation of 1-heptyne to 1-heptene. [Copyright &y& Elsevier]